Electrochemical detectors are now widely used in high performance liquid chromatography. Because of their sensitivity, dynamic range, and scope of application, they are often the detector-of-choice for analyses. For many health-related analyses, they cannot be used because of passivation of the electrode caused by accumulation of electrolysis products or unfavorable electron transfer kinetics. The program described herein addresses these problems by immobilization of electro- catalysts on electrode surfaces. The test species in this preliminary study are thiocyanate, which is an indicator of smoking behavior and a metabolite of certain drugs, and selected thiols and carbohydrates. This set is subject to the earlier- mentioned limitations at bare electrodes. The electrodes will be modified by mixed-metal inorganic films which comprise a catalyst, such as Ru(CN)64-, that is immobilized in a film matrix, such as osmium oxide. Preliminary results indicate that this approach to electrode modification will yield surfaces that possess the long term stability, both during usage and storage, to be the basis of practical sensors. A set of modified electrodes that covers a range of formal potentials is proposed. Generally ruthenium and osmium oxides will be the film matrices; the electron transfer mediators will be Ru(CN)64-, Fe(CN)64-, Mo(CN)84-, and IrCl62-. A stable form of iridium oxide will also be used as an electrode modifier since our preliminary results suggest that it both catalyzes electron transfer and acts as a source and sink of oxygen in electrode reactions.